The present invention relates to abrasive particles and methods of making the same. The abrasive particles may be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
There are a variety of abrasive particles (e.g., diamond particles, cubic boron nitride particles, fused abrasive particles (including fused alumina, heat treated fused alumina, fused alumina zirconia, and the like), and sintered, ceramic abrasive particles (including sol-gel-derived abrasive particles) known in the art. In some abrading applications, the abrasive particles are used in loose form or a slurry, while in others the particles are incorporated into abrasive products (including: bonded abrasives, coated abrasives and nonwoven abrasives).
Bonded abrasives typically comprise a plurality of abrasive particles bonded together to form a shaped mass. Coated abrasives typically comprise a plurality of abrasive particles bonded to a backing. Nonwoven abrasives typically comprise a plurality of abrasive particles bonded onto and into a lofty, porous, nonwoven substrate. Typical bonding materials for bonded abrasives are organic binders, vitreous binders, and metallic binders, while for coated and nonwoven abrasives they are typically organic binders. Criteria used in selecting abrasive particles used for a particular abrading application typically include: abrading life, rate of cut, substrate surface finish, grinding efficiency, and product cost.
The abrasive industry and their customers are continually looking for ways to improve one or more of these abrading criteria. For the past one hundred years or so, fused alumina abrasive particles have been widely utilized. Fused alumina abrasive particles are typically made by charging a furnace with an alumina source (such as aluminum ore or bauxite), as well as other desired additives, heating the material above its melting point, cooling the melt to provide a solidified mass, crushing the solidified mass into particles, and then screening and grading the particles to provide the desired abrasive particle size distribution. Over the past thirty years or so, there have been numerous developments concerning abrasive particles, including fused alumina zirconia abrasive particles (see, e.g., U.S. Pat. No. 3,891,408 (Rowse et al.); U.S. Pat. No. 3,781,172 (Pett et al.); U.S. Pat. No. 3,893,826 (Quinan et al.); U.S. Pat. No. 4,059,417 (Ilmaier et al.); U.S. Pat. No. 4,126,429 (Watson); U.S. Pat. No. 4,457,767 (Poon et al.); U.S. Pat. No. 5,143,522 (Gibson et al.); and U.S. Pat. No. 5,248,318 (Tamamki et al.)) and fused zirconia abrasives particles (see, e.g., U.S. Pat. No. 3,996,702 (Leahy) and Reissued U.S. Pat. No. Re 31,620 (Leahy)).
Although fused alpha alumina abrasive particles and fused alumina-zirconia abrasive particles are still widely used in abrading applications (including those utilizing coated and bonded abrasive products), the premier abrasive particles for many abrading applications since about the mid-1980""s are sol-gel-derived alpha alumina particles (also referred to as sintered, ceramic alpha alumina particles). (See e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 4,960,441 (Pellow et al.), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963 (Larmie), and U.S. Pat. No. 5,725,162 (Garg et al.)). Optionally, the sol-gel-derived alpha alumina may contain one or more secondary phases, including zirconia, up to about 60 percent by weight of the abrasive particle. (See e.g., JP 07-215708, xe2x80x9cComplex Compounds of Hydrazine Used to Prepare Solid Solution Powders, Materials, Alumina-Zirconia Ceramics, and Alumina-Zirconia Abrasive Grainsxe2x80x9d, August 1995).
Traditionally, it has been thought that in order to obtain acceptable cut rates for a given workpiece, abrasive particles having a relatively high hardness and toughness must be used in an abrasive article. Hardness relates to an abrasive particle""s ability to penetrate a workpiece, such as a metal, and cause chip removal from the workpiece. Toughness relates to an abrasive particle""s ability to withstand forces during an abrading process such that the abrasive particle does not fracture. Conventional wisdom in the abrasives industry has placed a significant emphasis on the hardness of an abrasive particle. For example, Milton Shaw, in his text xe2x80x9cPrinciples of Abrasive Processing,xe2x80x9d Oxford University Press, New York, N.Y. (1996), states, xe2x80x9cSince the relative hardness of the contacting bodies is of prime importance in determining abrasive wear, abrasives of high hardness are desired.xe2x80x9d Furthermore, for example, Stephen Krar and Ernest Ratterman, in their text xe2x80x9cSuperabrasives: Grinding and Machining with CBN and Diamond,xe2x80x9d Glencoe/McGraw-Hill, Westerville, Ohio (1990), state, xe2x80x9cThe hardness property is very important for an abrasive. The harder the abrasive with respect to the workpiece, the more easily it can cut.xe2x80x9d The two major conventional abrasives, alumina and silicon carbide, have hardness values of about 16-22 GPa and 25-30 GPa, respectively. The two major superabrasives, diamond and cubic boron nitride, have hardness values well in excess of 40 GPa. Thus, softer abrasive materials, such as zirconia (hardness values of about 12-13 GPa), with hardness values below those of these common abrasives, have traditionally not generally been considered very useful in metal removal applications and were believed unable to provide acceptable cut rates on most workpieces.
There is a continuous effort to improve the abrading characteristics of abrasive particles. Properties such as abrasive particle hardness and toughness, cost of producing, and performance characteristics continue to be taken into account when selecting and developing given abrasive particles. Typically, the most important performance criteria when selecting a given abrasive particle and abrasive article is the amount of work that a given abrasive particle and article containing the same can do prior to failure.
What is needed in the art is an abrasive particle that provides improved work performance and lifetime over conventional abrasive particles on one or more given workpieces. Further, what is needed in the art is an abrasive article, which provides exceptional abrading performance as measured by amount and rate of workpiece abraded.
The present invention provides abrasive particles comprising zirconia. In one aspect, the present invention provides abrasive particles comprising at least 60 (65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, or even 100) parts by weight of sintered polycrystalline zirconia based on the total weight of the abrasive particle. For certain abrasive particles according to the present invention, the zirconia is at least partially stabilized.
In another aspect, the present invention provides a plurality of particles having a particle size distribution ranging from fine to coarse, wherein at least a portion of the plurality of particles are abrasive particles according to the present invention.
In another aspect, the present invention provides a method of making abrasive particles containing at least 60 percent by weight of sintered, polycrystalline zirconia, based on the total weight of the abrasive particle. One method of making abrasive particles of the present invention comprises the following steps: (1) preparing an abrasive particle composition comprising at least 60 percent by weight of polycrystalline zirconia, based on the total weight of the abrasive particle composition; (2) sintering the abrasive particle composition to form one or more sintered articles; and (3) converting the one or more sintered articles to sintered, polycrystalline abrasive particles, wherein the abrasive particle composition is processed at one or more processing temperatures in the above steps, and wherein the one or more processing temperatures is less than a melting temperature of the abrasive particle composition.
In yet another aspect, the present invention provides a method of abrading a surface, wherein the method includes the step of contacting at least one abrasive particle comprising at least 60 percent by weight of sintered, polycrystalline zirconia, based on a total weight of the abrasive particle, with a surface of a workpiece.
Abrasive particles according to the present invention can be incorporated, for example, into abrasive articles, such as coated abrasive products, bonded abrasive products, nonwoven abrasive products, and abrasive brushes.
Embodiments of the present invention include abrasive particles having exceptional abrading properties, alone or when incorporated into an abrasive article, even though the abrasive particles having a relatively low hardness. In another aspect, embodiments of the present invention include abrasive particles having exceptional strength and toughness.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.